Modeling of corrosion for steel structures in sea or estuary area is still a great challenge in view to analyze their safety and optimize their maintenance. Several inspection campaigns have been performed during the three last decades in some French harbours. Thus a great number of ultrasonic residual measurements are now available for structures in various environments. This information allows to perform a statistical analysis in view to best understand and model the distribution of loss of matter on those structures according to different areas (mainly tidal and immersion areas). Results confirm that the loss of thickness is higher at the interface between the tidal area and immersion area. An analysis of the spatial process is performed: stationarity is analyzed on three marine structures where the amount of data is significant. Finally, a first level of spatial dependent corrosion modeling of steel in marine environment is suggested.